Water-insoluble hydrogels have been proposed for use in absorbent structures. A major drawback of the hydrogel materials is their relatively high cost, as compared to conventional absorbent materials like cotton and wood pulp fibers. A second drawback is a phenomenon called gel-blocking: when exposed to a fluid, the outer layers of a hydrogel particle swell, thus preventing fluid to reach the inner layers of the particle other than by a relatively slow diffusion process. Because of this gel blocking, hydrogel materials have relatively poor absorption kinetics.
One general approach towards solving this problem is to provide a multilayer structure, comprising one or more hydrogel containing layers and one or more wicking layers.
Examples of this approach are disclosed in: U.S. Pat. No. 4,364,992, issued Dec. 21, 1982 to Ito et al; U.S. Pat. No. 4,102,340, issued Jul. 25, 1978 to Mesek et al; and in EP-PA 83306764.8, publication No. 0 108 637.
A drawback of this approach is that the wicking layer does not have the excellent rewet properties of hydrogel material. Another drawback is the relatively high manufacturing cost of multilayer structures.
EP PA 8430 1578.5, publication No., 0 122 042, discloses absorbent structures comprised of a hydrophilic fibrous matrix having dispersed therein discrete particles of a water-insoluble hydrogel material. The structures are compressed to a relatively high density, so as to ensure good wicking.
Although this latter approach provides absorbent structures having a good performance in terms of rewet and absorbent capacity, there is still room for improvement. The high cost of hydrogel materials make a further increase of the absorbent capacity per gram of material highly desirable.
It is therefore an object of the present invention to provide a hydrogel-comprising absorbent structure having an improved absorbent capacity per gram of hydrogel material used.